1. Field of the Invention
The present invention relates to an amplifier, and in particular, it relates to an amplifier that changes the frequency to detect adjacent channel leakage power (ACP) without using a pilot signal when a difference in level between carriers occurs, to compensate for distortion by a stable feedforward (FF) control.
2. Description of the Related Art
Referring to FIG. 12, a general feedforward amplifier (FF amplifier) will be described. FIG. 12 is a block diagram showing the basic structure of a related-art FF amplifier.
As shown in FIG. 12, the related-art amplifier includes a first directional coupler 1, a first vector controller 2, a main amplifier 3 for amplifying an input signal, a second directional coupler 4, a first delay line 5, a second vector controller 6, an auxiliary amplifier 7, a second delay line 8, a third directional coupler 9, a distortion detector 10, a controller 11, a fourth directional coupler 12, a pilot receiver 13, and a pilot signal generator 14.
In the amplifier, a distortion detection loop is constructed of the first directional coupler 1, the first vector controller 2, the main amplifier 3 for amplifying an input signal, the second directional coupler 4, the first delay line 5, the distortion detector 10, and the controller 11; a distortion elimination loop is constructed of the second directional coupler 4, the second vector controller 6, the auxiliary amplifier 7, the second delay line 8, the third directional coupler 9, the controller 11, the fourth directional coupler 12, and the pilot receiver 13.
In the amplifier, the first and second vector controllers 2 and 6 include a variable attenuator and a variable phase shifter and controls the balance of the loops.
Of the inputted signal, the base signal is suppressed to extract only distortion by balancing the distortion detection loop by the operation of the first vector controller 2. The base signal means an inputted signal component.
The distortion detector 10 measures the suppression of the base signal. The first vector controller 2 is controlled automatically by the controller 11 so that the measurement becomes the minimum.
In the path of the second delay line 8, the base signal amplified by the main amplifier 3 has distortion. The pilot signal generator 14 delivers a pilot signal into the distortion detection loop. The pilot receiver 13 receives the pilot signal via the fourth directional coupler 12. The controller 11 controls the second vector controller 6 automatically so that the level of the pilot signal becomes the minimum.
The balance of the two loops is controlled by the two detectors of the distortion detector 10 and the pilot receiver 13, the controller 11, and the first and second vector controllers 2 and 6 in the loops, so that the distortion in the path of the second delay line 8 and extracted distortion are combined in opposite phase by the third directional coupler 9, so that the base signal without distortion is amplified to a specified level at the output (OUT).
FIG. 13 is spectral graph of the input signal and the output signal of the amplifier, respectively. FIG. 13 shows the generation of ACP. In the drawings, frequency is plotted in abscissa and signal level in ordinate. Since the output signal in ordinate is larger than the input signal in ordinate because the output signal is amplified. The dotted line of the output signal is shown in schematic form in assumption that the amplifier amplifies the signal linearly without generating distortion.
When a wideband signal as in wideband code division multiple access (W-CDMA) is amplified, ACP is generated as intermodulation distortion (IM) in the vicinity of the input signal as shown in FIG. 13.
Also with the FF amplifier, the base signal in the output signal of the main amplifier 3 is distorted, as shown in FIG. 13. When the distortion elimination loop is controlled so as to lower the ACP level as in the foregoing method in which the IM (ACP) level in the vicinity of the base signal is received by the pilot receiver 13 and the pilot signal is used, there is no need to use the pilot signal. The structure of an amplifier that uses no pilot signal is shown in FIG. 14. FIG. 14 is a block diagram of an FF amplifier of a frequency-fixed ACP reception system.
There is another related-art distortion compensation amplifiers. FIG. 11 is a block diagram showing the structure of another related-art distortion compensation amplifier.
The distortion compensation amplifier of FIG. 11 includes a distortion compensating circuit 21 that compensates for the distortion of an input signal, a main amplifier 22 that amplifies the inputted signal, a directional coupler 23 that divides the inputted signal, a distortion detector 24 that detects the level of the ACP in the amplified signal, and a controller 25 that controls the compensation of the distortion compensating circuit 21.
The distortion compensation amplifier of FIG. 11 compensates for distortion in such a way that, because IM (ACP) is generated in the output of the main amplifier 22, a feedback loop is constructed in which the controller 25 controls the distortion compensating circuit 21 so that the ACP level detected by the distortion detector 24 is reduced.
Related-art distortion compensation amplifiers include a distortion compensation amplifier published in JP-A-2003-283259, Oct. 3, 2003, (Applicant: Hitachi Kokusai Electric Inc., Inventor: Junya Dosaka).
This related-art distortion compensation amplifier is a feedforward amplifier that uses a pilot signal for a multicarrier.